Adding upstream version 16.2.11+ds.upstream/16.2.11+dsupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 600 insertions, 0 deletions

diff --git a/src/mds/flock.cc b/src/mds/flock.cc
new file mode 100644
index 000000000..69d579d30
--- /dev/null
+++ b/src/mds/flock.cc
@@ -0,0 +1,600 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+#include <errno.h>
+
+#include "common/debug.h"
+#include "mdstypes.h"
+#include "mds/flock.h"
+
+#define dout_subsys ceph_subsys_mds
+
+using std::list;
+using std::pair;
+using std::multimap;
+
+static multimap<ceph_filelock, ceph_lock_state_t*> global_waiting_locks;
+
+static void remove_global_waiting(ceph_filelock &fl, ceph_lock_state_t *lock_state)
+{
+  for (auto p = global_waiting_locks.find(fl);
+       p != global_waiting_locks.end(); ) {
+    if (p->first != fl)
+      break;
+    if (p->second == lock_state) {
+      global_waiting_locks.erase(p);
+      break;
+    }
+    ++p;
+  }
+}
+
+ceph_lock_state_t::~ceph_lock_state_t()
+{
+  if (type == CEPH_LOCK_FCNTL) {
+    for (auto p = waiting_locks.begin(); p != waiting_locks.end(); ++p) {
+      remove_global_waiting(p->second, this);
+    }
+  }
+}
+
+bool ceph_lock_state_t::is_waiting(const ceph_filelock &fl) const
+{
+  auto p = waiting_locks.find(fl.start);
+  while (p != waiting_locks.end()) {
+    if (p->second.start > fl.start)
+      return false;
+    if (p->second.length == fl.length &&
+	ceph_filelock_owner_equal(p->second, fl))
+      return true;
+    ++p;
+  }
+  return false;
+}
+
+void ceph_lock_state_t::remove_waiting(const ceph_filelock& fl)
+{
+  for (auto p = waiting_locks.find(fl.start);
+       p != waiting_locks.end(); ) {
+    if (p->second.start > fl.start)
+      break;
+    if (p->second.length == fl.length &&
+	ceph_filelock_owner_equal(p->second, fl)) {
+      if (type == CEPH_LOCK_FCNTL) {
+	remove_global_waiting(p->second, this);
+      }
+      waiting_locks.erase(p);
+      --client_waiting_lock_counts[(client_t)fl.client];
+      if (!client_waiting_lock_counts[(client_t)fl.client]) {
+        client_waiting_lock_counts.erase((client_t)fl.client);
+      }
+      break;
+    }
+    ++p;
+  }
+}
+
+bool ceph_lock_state_t::is_deadlock(const ceph_filelock& fl,
+				    list<multimap<uint64_t, ceph_filelock>::iterator>&
+				      overlapping_locks,
+				    const ceph_filelock *first_fl, unsigned depth) const
+{
+  ldout(cct,15) << "is_deadlock " << fl << dendl;
+
+  // only for posix lock
+  if (type != CEPH_LOCK_FCNTL)
+    return false;
+
+  // find conflict locks' owners
+  std::set<ceph_filelock> lock_owners;
+  for (auto p = overlapping_locks.begin();
+       p != overlapping_locks.end();
+       ++p) {
+
+    if (fl.type == CEPH_LOCK_SHARED &&
+	(*p)->second.type == CEPH_LOCK_SHARED)
+      continue;
+
+    // circle detected
+    if (first_fl && ceph_filelock_owner_equal(*first_fl, (*p)->second)) {
+      ldout(cct,15) << " detect deadlock" << dendl;
+      return true;
+    }
+
+    ceph_filelock tmp = (*p)->second;
+    tmp.start = 0;
+    tmp.length = 0;
+    tmp.type = 0;
+    lock_owners.insert(tmp);
+  }
+
+  if (depth >= MAX_DEADLK_DEPTH)
+    return false;
+
+  first_fl = first_fl ? first_fl : &fl;
+  for (auto p = lock_owners.begin();
+       p != lock_owners.end();
+       ++p) {
+    ldout(cct,15) << " conflict lock owner " << *p << dendl;
+    // if conflict lock' owner is waiting for other lock?
+    for (auto q = global_waiting_locks.lower_bound(*p);
+	 q != global_waiting_locks.end();
+	 ++q) {
+      if (!ceph_filelock_owner_equal(q->first, *p))
+	break;
+
+      list<multimap<uint64_t, ceph_filelock>::iterator>
+	_overlapping_locks, _self_overlapping_locks;
+      ceph_lock_state_t& state = *(q->second);
+      if (state.get_overlapping_locks(q->first, _overlapping_locks)) {
+	state.split_by_owner(q->first, _overlapping_locks, _self_overlapping_locks);
+      }
+      if (!_overlapping_locks.empty()) {
+	if (is_deadlock(q->first, _overlapping_locks, first_fl, depth + 1))
+	  return true;
+      }
+    }
+  }
+  return false;
+}
+
+void ceph_lock_state_t::add_waiting(const ceph_filelock& fl)
+{
+  waiting_locks.insert(pair<uint64_t, ceph_filelock>(fl.start, fl));
+  ++client_waiting_lock_counts[(client_t)fl.client];
+  if (type == CEPH_LOCK_FCNTL) {
+    global_waiting_locks.insert(pair<ceph_filelock,ceph_lock_state_t*>(fl, this));
+  }
+}
+
+bool ceph_lock_state_t::add_lock(ceph_filelock& new_lock,
+                                 bool wait_on_fail, bool replay,
+				 bool *deadlock)
+{
+  ldout(cct,15) << "add_lock " << new_lock << dendl;
+  bool ret = false;
+  list<multimap<uint64_t, ceph_filelock>::iterator>
+    overlapping_locks, self_overlapping_locks, neighbor_locks;
+
+  // first, get any overlapping locks and split them into owned-by-us and not
+  if (get_overlapping_locks(new_lock, overlapping_locks, &neighbor_locks)) {
+    ldout(cct,15) << "got overlapping lock, splitting by owner" << dendl;
+    split_by_owner(new_lock, overlapping_locks, self_overlapping_locks);
+  }
+  if (!overlapping_locks.empty()) { //overlapping locks owned by others :(
+    if (CEPH_LOCK_EXCL == new_lock.type) {
+      //can't set, we want an exclusive
+      ldout(cct,15) << "overlapping lock, and this lock is exclusive, can't set"
+              << dendl;
+      if (wait_on_fail && !replay) {
+	if (is_deadlock(new_lock, overlapping_locks))
+	  *deadlock = true;
+	else
+	  add_waiting(new_lock);
+      }
+    } else { //shared lock, check for any exclusive locks blocking us
+      if (contains_exclusive_lock(overlapping_locks)) { //blocked :(
+        ldout(cct,15) << " blocked by exclusive lock in overlapping_locks" << dendl;
+	if (wait_on_fail && !replay) {
+	  if (is_deadlock(new_lock, overlapping_locks))
+	    *deadlock = true;
+	  else
+	    add_waiting(new_lock);
+	}
+      } else {
+        //yay, we can insert a shared lock
+        ldout(cct,15) << "inserting shared lock" << dendl;
+        remove_waiting(new_lock);
+        adjust_locks(self_overlapping_locks, new_lock, neighbor_locks);
+        held_locks.insert(pair<uint64_t, ceph_filelock>(new_lock.start, new_lock));
+        ret = true;
+      }
+    }
+  } else { //no overlapping locks except our own
+    remove_waiting(new_lock);
+    adjust_locks(self_overlapping_locks, new_lock, neighbor_locks);
+    ldout(cct,15) << "no conflicts, inserting " << new_lock << dendl;
+    held_locks.insert(pair<uint64_t, ceph_filelock>
+                      (new_lock.start, new_lock));
+    ret = true;
+  }
+  if (ret) {
+    ++client_held_lock_counts[(client_t)new_lock.client];
+  }
+  return ret;
+}
+
+void ceph_lock_state_t::look_for_lock(ceph_filelock& testing_lock)
+{
+  list<multimap<uint64_t, ceph_filelock>::iterator> overlapping_locks,
+    self_overlapping_locks;
+  if (get_overlapping_locks(testing_lock, overlapping_locks)) {
+    split_by_owner(testing_lock, overlapping_locks, self_overlapping_locks);
+  }
+  if (!overlapping_locks.empty()) { //somebody else owns overlapping lock
+    if (CEPH_LOCK_EXCL == testing_lock.type) { //any lock blocks it
+      testing_lock = (*overlapping_locks.begin())->second;
+    } else {
+      ceph_filelock *blocking_lock;
+      if ((blocking_lock = contains_exclusive_lock(overlapping_locks))) {
+        testing_lock = *blocking_lock;
+      } else { //nothing blocking!
+        testing_lock.type = CEPH_LOCK_UNLOCK;
+      }
+    }
+    return;
+  }
+  //if we get here, only our own locks block
+  testing_lock.type = CEPH_LOCK_UNLOCK;
+}
+
+void ceph_lock_state_t::remove_lock(ceph_filelock removal_lock,
+                 list<ceph_filelock>& activated_locks)
+{
+  list<multimap<uint64_t, ceph_filelock>::iterator> overlapping_locks,
+    self_overlapping_locks;
+  if (get_overlapping_locks(removal_lock, overlapping_locks)) {
+    ldout(cct,15) << "splitting by owner" << dendl;
+    split_by_owner(removal_lock, overlapping_locks, self_overlapping_locks);
+  } else ldout(cct,15) << "attempt to remove lock at " << removal_lock.start
+                 << " but no locks there!" << dendl;
+  bool remove_to_end = (0 == removal_lock.length);
+  uint64_t removal_start = removal_lock.start;
+  uint64_t removal_end = removal_start + removal_lock.length - 1;
+  __s64 old_lock_client = 0;
+  ceph_filelock *old_lock;
+
+  ldout(cct,15) << "examining " << self_overlapping_locks.size()
+          << " self-overlapping locks for removal" << dendl;
+  for (list<multimap<uint64_t, ceph_filelock>::iterator>::iterator
+         iter = self_overlapping_locks.begin();
+       iter != self_overlapping_locks.end();
+       ++iter) {
+    ldout(cct,15) << "self overlapping lock " << (*iter)->second << dendl;
+    old_lock = &(*iter)->second;
+    bool old_lock_to_end = (0 == old_lock->length);
+    uint64_t old_lock_end = old_lock->start + old_lock->length - 1;
+    old_lock_client = old_lock->client;
+    if (remove_to_end) {
+      if (old_lock->start < removal_start) {
+        old_lock->length = removal_start - old_lock->start;
+      } else {
+        ldout(cct,15) << "erasing " << (*iter)->second << dendl;
+        held_locks.erase(*iter);
+        --client_held_lock_counts[old_lock_client];
+      }
+    } else if (old_lock_to_end) {
+      ceph_filelock append_lock = *old_lock;
+      append_lock.start = removal_end+1;
+      held_locks.insert(pair<uint64_t, ceph_filelock>
+                        (append_lock.start, append_lock));
+      ++client_held_lock_counts[(client_t)old_lock->client];
+      if (old_lock->start >= removal_start) {
+        ldout(cct,15) << "erasing " << (*iter)->second << dendl;
+        held_locks.erase(*iter);
+        --client_held_lock_counts[old_lock_client];
+      } else old_lock->length = removal_start - old_lock->start;
+    } else {
+      if (old_lock_end  > removal_end) {
+        ceph_filelock append_lock = *old_lock;
+        append_lock.start = removal_end + 1;
+        append_lock.length = old_lock_end - append_lock.start + 1;
+        held_locks.insert(pair<uint64_t, ceph_filelock>
+                          (append_lock.start, append_lock));
+        ++client_held_lock_counts[(client_t)old_lock->client];
+      }
+      if (old_lock->start < removal_start) {
+        old_lock->length = removal_start - old_lock->start;
+      } else {
+        ldout(cct,15) << "erasing " << (*iter)->second << dendl;
+        held_locks.erase(*iter);
+        --client_held_lock_counts[old_lock_client];
+      }
+    }
+    if (!client_held_lock_counts[old_lock_client]) {
+      client_held_lock_counts.erase(old_lock_client);
+    }
+  }
+}
+
+bool ceph_lock_state_t::remove_all_from (client_t client)
+{
+  bool cleared_any = false;
+  if (client_held_lock_counts.count(client)) {
+    multimap<uint64_t, ceph_filelock>::iterator iter = held_locks.begin();
+    while (iter != held_locks.end()) {
+      if ((client_t)iter->second.client == client) {
+	held_locks.erase(iter++);
+      } else
+	++iter;
+    }
+    client_held_lock_counts.erase(client);
+    cleared_any = true;
+  }
+
+  if (client_waiting_lock_counts.count(client)) {
+    multimap<uint64_t, ceph_filelock>::iterator iter = waiting_locks.begin();
+    while (iter != waiting_locks.end()) {
+      if ((client_t)iter->second.client != client) {
+	++iter;
+	continue;
+      }
+      if (type == CEPH_LOCK_FCNTL) {
+	remove_global_waiting(iter->second, this);
+      }
+      waiting_locks.erase(iter++);
+    }
+    client_waiting_lock_counts.erase(client);
+  }
+  return cleared_any;
+}
+
+void ceph_lock_state_t::adjust_locks(list<multimap<uint64_t, ceph_filelock>::iterator> old_locks,
+                  ceph_filelock& new_lock,
+                  list<multimap<uint64_t, ceph_filelock>::iterator>
+                  neighbor_locks)
+{
+  ldout(cct,15) << "adjust_locks" << dendl;
+  bool new_lock_to_end = (0 == new_lock.length);
+  __s64 old_lock_client = 0;
+  ceph_filelock *old_lock;
+  for (list<multimap<uint64_t, ceph_filelock>::iterator>::iterator
+         iter = old_locks.begin();
+       iter != old_locks.end();
+       ++iter) {
+    old_lock = &(*iter)->second;
+    ldout(cct,15) << "adjusting lock: " << *old_lock << dendl;
+    bool old_lock_to_end = (0 == old_lock->length);
+    uint64_t old_lock_start = old_lock->start;
+    uint64_t old_lock_end = old_lock->start + old_lock->length - 1;
+    uint64_t new_lock_start = new_lock.start;
+    uint64_t new_lock_end = new_lock.start + new_lock.length - 1;
+    old_lock_client = old_lock->client;
+    if (new_lock_to_end || old_lock_to_end) {
+      //special code path to deal with a length set at 0
+      ldout(cct,15) << "one lock extends forever" << dendl;
+      if (old_lock->type == new_lock.type) {
+        //just unify them in new lock, remove old lock
+        ldout(cct,15) << "same lock type, unifying" << dendl;
+        new_lock.start = (new_lock_start < old_lock_start) ? new_lock_start :
+          old_lock_start;
+        new_lock.length = 0;
+        held_locks.erase(*iter);
+        --client_held_lock_counts[old_lock_client];
+      } else { //not same type, have to keep any remains of old lock around
+        ldout(cct,15) << "shrinking old lock" << dendl;
+        if (new_lock_to_end) {
+          if (old_lock_start < new_lock_start) {
+            old_lock->length = new_lock_start - old_lock_start;
+          } else {
+            held_locks.erase(*iter);
+            --client_held_lock_counts[old_lock_client];
+          }
+        } else { //old lock extends past end of new lock
+          ceph_filelock appended_lock = *old_lock;
+          appended_lock.start = new_lock_end + 1;
+          held_locks.insert(pair<uint64_t, ceph_filelock>
+                            (appended_lock.start, appended_lock));
+          ++client_held_lock_counts[(client_t)old_lock->client];
+          if (old_lock_start < new_lock_start) {
+            old_lock->length = new_lock_start - old_lock_start;
+          } else {
+            held_locks.erase(*iter);
+            --client_held_lock_counts[old_lock_client];
+          }
+        }
+      }
+    } else {
+      if (old_lock->type == new_lock.type) { //just merge them!
+        ldout(cct,15) << "merging locks, they're the same type" << dendl;
+        new_lock.start = (old_lock_start < new_lock_start ) ? old_lock_start :
+          new_lock_start;
+        int new_end = (new_lock_end > old_lock_end) ? new_lock_end :
+          old_lock_end;
+        new_lock.length = new_end - new_lock.start + 1;
+        ldout(cct,15) << "erasing lock " << (*iter)->second << dendl;
+        held_locks.erase(*iter);
+        --client_held_lock_counts[old_lock_client];
+      } else { //we'll have to update sizes and maybe make new locks
+        ldout(cct,15) << "locks aren't same type, changing sizes" << dendl;
+        if (old_lock_end > new_lock_end) { //add extra lock after new_lock
+          ceph_filelock appended_lock = *old_lock;
+          appended_lock.start = new_lock_end + 1;
+          appended_lock.length = old_lock_end - appended_lock.start + 1;
+          held_locks.insert(pair<uint64_t, ceph_filelock>
+                            (appended_lock.start, appended_lock));
+          ++client_held_lock_counts[(client_t)old_lock->client];
+        }
+        if (old_lock_start < new_lock_start) {
+          old_lock->length = new_lock_start - old_lock_start;
+        } else { //old_lock starts inside new_lock, so remove it
+          //if it extended past new_lock_end it's been replaced
+          held_locks.erase(*iter);
+          --client_held_lock_counts[old_lock_client];
+        }
+      }
+    }
+    if (!client_held_lock_counts[old_lock_client]) {
+      client_held_lock_counts.erase(old_lock_client);
+    }
+  }
+
+  //make sure to coalesce neighboring locks
+  for (list<multimap<uint64_t, ceph_filelock>::iterator>::iterator
+         iter = neighbor_locks.begin();
+       iter != neighbor_locks.end();
+       ++iter) {
+    old_lock = &(*iter)->second;
+    old_lock_client = old_lock->client;
+    ldout(cct,15) << "lock to coalesce: " << *old_lock << dendl;
+    /* because if it's a neighboring lock there can't be any self-overlapping
+       locks that covered it */
+    if (old_lock->type == new_lock.type) { //merge them
+      if (0 == new_lock.length) {
+        if (old_lock->start + old_lock->length == new_lock.start) {
+          new_lock.start = old_lock->start;
+        } else ceph_abort(); /* if there's no end to new_lock, the neighbor
+                             HAS TO be to left side */
+      } else if (0 == old_lock->length) {
+        if (new_lock.start + new_lock.length == old_lock->start) {
+          new_lock.length = 0;
+        } else ceph_abort(); //same as before, but reversed
+      } else {
+        if (old_lock->start + old_lock->length == new_lock.start) {
+          new_lock.start = old_lock->start;
+          new_lock.length = old_lock->length + new_lock.length;
+        } else if (new_lock.start + new_lock.length == old_lock->start) {
+          new_lock.length = old_lock->length + new_lock.length;
+        }
+      }
+      held_locks.erase(*iter);
+      --client_held_lock_counts[old_lock_client];
+    }
+    if (!client_held_lock_counts[old_lock_client]) {
+      client_held_lock_counts.erase(old_lock_client);
+    }
+  }
+}
+
+multimap<uint64_t, ceph_filelock>::iterator
+ceph_lock_state_t::get_lower_bound(uint64_t start,
+                                   multimap<uint64_t, ceph_filelock>& lock_map)
+{
+   multimap<uint64_t, ceph_filelock>::iterator lower_bound =
+     lock_map.lower_bound(start);
+   if ((lower_bound->first != start)
+       && (start != 0)
+       && (lower_bound != lock_map.begin())) --lower_bound;
+   if (lock_map.end() == lower_bound)
+     ldout(cct,15) << "get_lower_dout(15)eturning end()" << dendl;
+   else ldout(cct,15) << "get_lower_bound returning iterator pointing to "
+                << lower_bound->second << dendl;
+   return lower_bound;
+ }
+
+multimap<uint64_t, ceph_filelock>::iterator
+ceph_lock_state_t::get_last_before(uint64_t end,
+                                   multimap<uint64_t, ceph_filelock>& lock_map)
+{
+  multimap<uint64_t, ceph_filelock>::iterator last =
+    lock_map.upper_bound(end);
+  if (last != lock_map.begin()) --last;
+  if (lock_map.end() == last)
+    ldout(cct,15) << "get_last_before returning end()" << dendl;
+  else ldout(cct,15) << "get_last_before returning iterator pointing to "
+               << last->second << dendl;
+  return last;
+}
+
+bool ceph_lock_state_t::share_space(
+    multimap<uint64_t, ceph_filelock>::iterator& iter,
+    uint64_t start, uint64_t end)
+{
+  bool ret = ((iter->first >= start && iter->first <= end) ||
+              ((iter->first < start) &&
+               (((iter->first + iter->second.length - 1) >= start) ||
+                (0 == iter->second.length))));
+  ldout(cct,15) << "share_space got start: " << start << ", end: " << end
+          << ", lock: " << iter->second << ", returning " << ret << dendl;
+  return ret;
+}
+
+bool ceph_lock_state_t::get_overlapping_locks(const ceph_filelock& lock,
+                           list<multimap<uint64_t,
+                               ceph_filelock>::iterator> & overlaps,
+                           list<multimap<uint64_t,
+                               ceph_filelock>::iterator> *self_neighbors)
+{
+  ldout(cct,15) << "get_overlapping_locks" << dendl;
+  // create a lock starting one earlier and ending one later
+  // to check for neighbors
+  ceph_filelock neighbor_check_lock = lock;
+  if (neighbor_check_lock.start != 0) {
+    neighbor_check_lock.start = neighbor_check_lock.start - 1;
+    if (neighbor_check_lock.length)
+      neighbor_check_lock.length = neighbor_check_lock.length + 2;
+  } else {
+    if (neighbor_check_lock.length)
+      neighbor_check_lock.length = neighbor_check_lock.length + 1;
+  }
+  //find the last held lock starting at the point after lock
+  uint64_t endpoint = lock.start;
+  if (lock.length) {
+    endpoint += lock.length;
+  } else {
+    endpoint = uint64_t(-1); // max offset
+  }
+  multimap<uint64_t, ceph_filelock>::iterator iter =
+    get_last_before(endpoint, held_locks);
+  bool cont = iter != held_locks.end();
+  while(cont) {
+    if (share_space(iter, lock)) {
+      overlaps.push_front(iter);
+    } else if (self_neighbors &&
+	       ceph_filelock_owner_equal(neighbor_check_lock, iter->second) &&
+               share_space(iter, neighbor_check_lock)) {
+      self_neighbors->push_front(iter);
+    }
+    if ((iter->first < lock.start) && (CEPH_LOCK_EXCL == iter->second.type)) {
+      //can't be any more overlapping locks or they'd interfere with this one
+      cont = false;
+    } else if (held_locks.begin() == iter) cont = false;
+    else --iter;
+  }
+  return !overlaps.empty();
+}
+
+bool ceph_lock_state_t::get_waiting_overlaps(const ceph_filelock& lock,
+                                             list<multimap<uint64_t,
+                                               ceph_filelock>::iterator>&
+                                               overlaps)
+{
+  ldout(cct,15) << "get_waiting_overlaps" << dendl;
+  multimap<uint64_t, ceph_filelock>::iterator iter =
+    get_last_before(lock.start + lock.length - 1, waiting_locks);
+  bool cont = iter != waiting_locks.end();
+  while(cont) {
+    if (share_space(iter, lock)) overlaps.push_front(iter);
+    if (waiting_locks.begin() == iter) cont = false;
+    --iter;
+  }
+  return !overlaps.empty();
+}
+
+void ceph_lock_state_t::split_by_owner(const ceph_filelock& owner,
+                                       list<multimap<uint64_t,
+                                           ceph_filelock>::iterator>& locks,
+                                       list<multimap<uint64_t,
+                                           ceph_filelock>::iterator>&
+                                           owned_locks)
+{
+  list<multimap<uint64_t, ceph_filelock>::iterator>::iterator
+    iter = locks.begin();
+  ldout(cct,15) << "owner lock: " << owner << dendl;
+  while (iter != locks.end()) {
+    ldout(cct,15) << "comparing to " << (*iter)->second << dendl;
+    if (ceph_filelock_owner_equal((*iter)->second, owner)) {
+      ldout(cct,15) << "success, pushing to owned_locks" << dendl;
+      owned_locks.push_back(*iter);
+      iter = locks.erase(iter);
+    } else {
+      ldout(cct,15) << "failure, something not equal in this group "
+              << (*iter)->second.client << ":" << owner.client << ","
+	      << (*iter)->second.owner << ":" << owner.owner << ","
+	      << (*iter)->second.pid << ":" << owner.pid << dendl;
+      ++iter;
+    }
+  }
+}
+
+ceph_filelock *
+ceph_lock_state_t::contains_exclusive_lock(list<multimap<uint64_t,
+                                               ceph_filelock>::iterator>& locks)
+{
+  for (list<multimap<uint64_t, ceph_filelock>::iterator>::iterator
+         iter = locks.begin();
+       iter != locks.end();
+       ++iter) {
+    if (CEPH_LOCK_EXCL == (*iter)->second.type) return &(*iter)->second;
+  }
+  return NULL;
+}